Study aim: The determination of therapeutic effect of bee propolis on the oral Lichen Planus treatment. Design: Clinical trial with control group, with parallel group, double-blind, randomized, phase 3 on 40 patients. The random numbers table was used to randomize. Settings and conduct: Patients who referred to the dental academic clinic or private centers in Bojnourd with OLP diagnosed by oral specialists, submit their initial information first and then in order to randomize the process, person "A" uses a computer and a table of random numbers to create a random sequence and people are divided into two "A" and "B" groups. Then, in the next step, person "B" prescribes medicine for one group and placebo for the other group. Group "A" consumes Propolis in the form of mouthwash with the dose of 500 mg according to the manufacturer's instructions and group "B", a placebo with the same form as the main drug is prescribed. The operator (the person prescribing the medicine) and the patient are not aware of any medicine or placebo. Participants/Inclusion and exclusion criteria: Inclusion criteria: Patients who are diagnosed with OLP by an oral specialist. People who have been willing to participate in the study and sign the informed consent form. Exclusion criteria: Patients with any past or present immunological disease or disorder. Patients with any past or present allergic disease or disorder. Pregnant and lactating women. Intervention groups: The Intervention Group consumes propolis in the form of mouthwash with the dose of 500 mg according to the manufacturer's instructions. The Control Group is given a placebo with a very similar form to the main drug and in the same way. Main outcome variables: Extent of Atrophic areas; Extent of Ulcerative areas; Extent of Keratotic areas; Intensity of pain and irritation; Type of intervention; Patient's Gender; Patient's age.